Common sources of errors in construction

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As we all know the evolution of the construction, it started with huts and shelters, constructed by hand or with simple tools. As cities grew during the Bronze Age, a class of professional craftsmen like bricklayers and carpenters appeared. Occasionally, slaves were used for construction work. In the middle ages, these were organized into guilds. In the 19th century, steam-powered machinery appeared, and later diesel- and electric powered vehicles such as cranes, excavators and bulldozers. Unlike before many things should be taken in to consideration from the design to execution, since the mankind demands a comfortable lifestyle. According to present scenario construction is no more a single activity, it involves multitasking. From construction manager to labor who lay the floor are all involved in the process of construction. There is every chance of making an error in the so called process.

There are many cases around which leads to loss in huge amounts from a well developed city like New York to ordinary city in developing country. Unlike before construction is no longer done by an individual team. This involves planning, designing, bidding, awarding, construction managers, sub contractors, suppliers, foreman, labor etc. In the process of going through all these any small error may prove costly. I like to discuss about the few types of errors that cause the construction industry a loss in terms of money or time. Too many errors in the contract process may lead the contractor to lose the money or to be competitive.


Main aim of project is to discuss about the errors that are generally caused during the construction process and to suggest some remedies to overcome those errors. Several stages of process include errors, which leads the party to be uncompetitive or to suffer a huge loss.

Most of the errors are caused during bidding process, while preparing the contract documents and also the union problems.


* Before estimating for the project, site visit is must for understanding the site conditions.

* Proper planning and inadequate knowledge about all the activities is the key for reducing errors.

* Calculation errors have to be reduced by using proper equipment.

* Labor wages has to be updated according to unions.

* Confirming that material suppliers are pricing properly.

* Efficient serviceable machines should be used to avoid delay.

* Using incorrect units has may lead to substantial loss.

* Agreement between the parties has to be made clear before the start of the project.

* Activities have to be properly linked to avoid the delay in the work.

Background & Methodology:

Estimates made on construction projects are arithmetical calculations of quantities and cost of materials and labor costs to install materials or perform various operations. In order to avoid errors in arithmetic, the estimator should use an electronic calculator with a recording tape, have the calculations checked by another person, and attach the tape to the estimate sheet for backup.Errors in measurements and dimensions taken from plans, drawings, and specifications result in corresponding mistakes in the cost of construction items based on those measurements.Hourly labor wages for construction workers vary countrywide. You should consistently verify current wage rates and fringe benefits for the building trades involved through local union offices, other contractors, supply yards, and other reliable sources. Overtime rates are generally one and one-half to two times regular rates depending on labor agreements and union rules.A frequent cause of error in estimating is allowing too much or too little for labor to do the job. Always be sure that building materials and supplies are correctly described as to kind, quality, size, and dimensions. Also confirm that they are priced competitively.Using a wrong unit of measure can result in substantial cost increases or decreases. For example, be careful not to record lineal feet for lineal yards, square feet for square yards or cubic feet for cubic yards, and so forth.Machinery or equipment to be used in construction, and included in the estimate or bid, must always be checked for efficient serviceability. Preparing an estimate on a construction project and contemplating the use of poorly maintained machinery or equipment is unwise. Breakdown, repairs, and idle time can be costly, delay completion of the project and invite penalties.

This source of error might well be number one on the list because of its importance in the early stages of cost estimating. Visiting the proposed site of the project enables the cost estimator to inspect topography, check the soil by boring if necessary, determine if protection of adjacent properties will be needed, and check distances to railroad sidings, supply centers, and the proximity to sources of labor. If existing structures have to be demolished or removed from the premises, the estimator is able to properly determine the probable cost.The cost of hauling materials, supplies, machinery, and equipment to a project can be a very expensive item in an estimate. Access to the job site may be difficult because of poor roads or no roads, heavy traffic to and from supply sources, or the requirement to obtain permits, and so forth.Cost estimates and bids on construction projects are subject to local, state and federal building codes, permits, and inspections. A contractor who is accustomed to working on projects that require high quality workmanship may not be set up to bid or estimate projects of mediocre, low grade workmanship. Conversely, a contractor who usually works on cheap structures is frequently at a disadvantage when it comes to bidding on the construction of upscale residences or commercial buildings where only the finest quality of workmanship is acceptable. Failure to give proper consideration to the quality of workmanship a project warrants can lead to overestimating or underestimating.Sometimes items such as scaffolding, ramps, and guardrails, are left out of an estimate on the assumption that their cost is relatively minor and can be absorbed in the overall bid. On small projects a contractor may gamble on his workers handling such items routinely. This can be a costly error. Subcontractors often prepare their cost estimates from the plans and specifications without the guidance or supervision of the general contractor. They take off details and include all of the items they assume to fall within their particular trade. As a result there frequently is overlapping with the work of the general contractor or other subcontractors.The owner looks to the general contractor for the completion of the work in compliance with the plans and specifications. The owner does not look to the subcontractors. It is very important that the estimates of subcontractors are carefully reviewed to be sure they comply with the plans and specifications.

Taking shortcuts when making an estimate can be risky. Often there is a temptation to take shortcuts when under pressure because of time-limit in which to complete the cost estimate or because of a heavy backlog of work. Shortcuts take the form of guesstimating, using square feet or cubic foot costs in place of details, and using lump sum figures picked out of the air, all of which have inherent risks. Not Allowing for Realistic Contingencies: Some construction projects may have inherent and unusual problems that should be recognized when the cost estimate is being prepared. Failure to make the allowances or contingencies may result in not getting the contract or losing money if awarded the contract. These contingencies include severe winter weather conditions, or extremely hot and humid climates. The project may be located in an area of the country subject to heavy rainfall. Justifications for a realistic contingency include anticipated labor troubles, material shortages, or political problems.A opposed to making allowances for realistic contingencies, it is poor policy to make flat allowances for contingencies without good reasons, particularly when competition is strong.

No one should put together a project schedule without knowing Critical Path Method concepts such as forward and backward pass, free float and total float. Many schedulers use the 8/80 rule, which stipulates that a task should not take fewer than eight hours or more than 80. As a best practice of construction scheduling, Lukas recommended using the 20/80 rule instead, as that cuts down on the number of tasks. Another option here is to create a sub-project schedule (such as a detailed design schedule) that is linked to the project schedule, Lukas said. Many dependent activities are programmed with a start-to-start lag when, in fact, they should have a finish-to-finish lag. Why? Let's say Task A takes four days and Task B takes five days but starts when Task A is 50% complete. If a scheduler assigns a start-to-start dependency, Task B will start on Day 3 even if Task A has been delayed for a week. With a finish-to-finish dependency, on the other hand, Task B will be set to finish three days after Task A, as it should, no matter what happens. A common error of construction scheduling is that, with the exception of Project Start and Project Complete, all tasks need at least one predecessor and one successor. To combat this, Lukas said, add a Successor column to a schedule's Gantt chart and scan it, as well as the Predecessor column, for any missing links.